Controlling the formation of a specific polymorphic form of active pharmaceutical ingredients,
particularly those that exhibit multiple polymorphic forms, during crystallization is critical for
pharmaceutical manufacturers. This paper describes the construction of a phase diagram using
Lasentec Focused Beam Reflectance Measurement (FBRM), which is an important step in the
development of an approach for polymorphic control of sulfathiazole, an antimicrobial agent that
is known to crystallize as a mixture of polymorphs. A preliminary work on mapping of different
regions in the phase diagram, where various polymorphic forms were found, is also reported
here. This study is part of a larger study on polymorphic control of pharmaceuticals through
supersaturation control using Process Analytical Technology.